linux-kernel - [PATCH v10 11/18] refcount: introduce __refcount_{add|inc}_not_zero_limited

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Message-ID: <20250213224655.1680278-12-surenb@google.com>
Date: Thu, 13 Feb 2025 14:46:48 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: peterz@...radead.org, willy@...radead.org, liam.howlett@...cle.com, 
	lorenzo.stoakes@...cle.com, david.laight.linux@...il.com, mhocko@...e.com, 
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	linux-doc@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	kernel-team@...roid.com, surenb@...gle.com
Subject: [PATCH v10 11/18] refcount: introduce __refcount_{add|inc}_not_zero_limited_acquire

Introduce functions to increase refcount but with a top limit above which
they will fail to increase (the limit is inclusive). Setting the limit to
INT_MAX indicates no limit.

Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
Changes since v9 [1]:
- Change refcount limit to be used with xxx_acquire functions

[1] https://lore.kernel.org/all/20250111042604.3230628-11-surenb@google.com/

 include/linux/refcount.h | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 4589d2e7bfea..80dc023ac2bf 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -213,13 +213,20 @@ static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)
 }
 
 static inline __must_check __signed_wrap
-bool __refcount_add_not_zero_acquire(int i, refcount_t *r, int *oldp)
+bool __refcount_add_not_zero_limited_acquire(int i, refcount_t *r, int *oldp,
+					     int limit)
 {
 	int old = refcount_read(r);
 
 	do {
 		if (!old)
 			break;
+
+		if (i > limit - old) {
+			if (oldp)
+				*oldp = old;
+			return false;
+		}
 	} while (!atomic_try_cmpxchg_acquire(&r->refs, &old, old + i));
 
 	if (oldp)
@@ -231,6 +238,18 @@ bool __refcount_add_not_zero_acquire(int i, refcount_t *r, int *oldp)
 	return old;
 }
 
+static inline __must_check bool
+__refcount_inc_not_zero_limited_acquire(refcount_t *r, int *oldp, int limit)
+{
+	return __refcount_add_not_zero_limited_acquire(1, r, oldp, limit);
+}
+
+static inline __must_check __signed_wrap
+bool __refcount_add_not_zero_acquire(int i, refcount_t *r, int *oldp)
+{
+	return __refcount_add_not_zero_limited_acquire(i, r, oldp, INT_MAX);
+}
+
 /**
  * refcount_add_not_zero_acquire - add a value to a refcount with acquire ordering unless it is 0
  *
-- 
2.48.1.601.g30ceb7b040-goog